X-ray tube



2. J. ATLEE Feb. 23, 1943.

X-RAY TUBE Filed April 25, 1941 1N\ ENTOR. BY Zkd J. 14221496 Patented Feb. 23, 1943 X-R-AY TUBE Zed J. Atlee, Elmhurst, Ill., assignor to General Electric X-Ray Corporation, Chicago, Ill., a corporation of New York Application April 25, 1941, Serial No. 390,322

7 Claims.

This invention relates in general to rotatable devices and has more particular reference to rotatable structures enclosed in sealed envelopes, the invention pertaining especially to an improved rotatable anode structure for use in X-ray tubes.

An important object of the present invention is to provide a rotating structure of the character mentioned, having a magnetic brake formed and arranged therein and operable normally to check rotary movement of the device; a further object being to form the braking means as a permanent magnet built into the rotary device and the mounting on which it is carried.

Another important object is to provide an improved braking system for controlling the rtation of a rotary anode in an X-ray tube.

Another important object resides in providing an improved mounting structure for a rotary de-. vice of the character mentioned; a further ob ject being to form the mounting as a hollow pedestal within which is journaled a turnable spindle carrying the rotatable device, whereby the pedestal may form a stationary mounting for carrying the magnet or other auxiliary equipment in position to co-operate with the rotary device; a

further object being to turnably support the carrying spindle in preferably roller bearings disposed within the hollow pedestal; a still further object being to provide means on the pedestal forlubricating the bearings therein and to control the application of lubricant from a position outwardly of the spindle.

Another important object is to provide for the accomplishment of the foregoing in a structure in which the rotary device comprises a tubular skirt portion embracing and enclosing not only the support pedestal but also all of the mechanism and auxiliary equipment mounted thereon.

These and numerous other important objects, advantages, and inherent functions of the invention will become apparent as the invention is more fully understood from the following description, which, taken in conjunction with the accompanying drawing, discloses a preferred embodiment of the invention.

Referring to the drawing:

Figure l is a sectional View through an X-ray tube provided with a rotating anode embodying my present invention; and

Figures 2 and 3 are views taken, respectively, along the lines 22 and 3-3 in Figure l.

To illustrate my invention, I have shown'on the drawing an X-ray generator ll comprising spaced-apart cathode and anode means l3 and l5 enclosed within a preferably glass envelope IT. The anode I5 is of the rotating type, being turnab y supported for rotation on mounting means l 9 which, in turn, is supported on the envelope l! at one end thereof. As shown, the envelope I! has an envelope extension 2! within which the anode I5 is snugly disposed, the envelope having a re-entrant sleeve-like portion 23 forming an annular space 25 between the envelope extension 2! and the re-entrant portion 23.

The mounting means I9 comprises a pedestal having a stem-like portion 21 extending outwardly of the envelope and a portion 29 extending within the envelope. The anode I5 is rotatably mounted on the portion 29, which is preferably hollow; and the pedestal is sealed to the envelope at the re-entrant portion 23, which defines an opening in which the pedestal extends. To this end, the pedestal is provided with an annular shoulder 3| carrying, sealed thereon, a plate or disk 32 having a cylindrical rim member 33 sealed at one end to the marginal edge of the disk 32, the opposite end of the rim member providing an-annular edge forming a glass-tometal seal 34 with the envelope at the inner end of the re-entrant envelope portion 23. This seal 34 supports the pedestal and the anode thereon in position embraced by the envelope extension 2|. The hollow pedestal portion 29 defines an axial cavity 35 extending within the pedestal and opening at the end thereof within the envelope, and the anode I5 is journaled on the inwardly extending portions of the pedestal.

It should be understood that X-ray generators function to produce X-rays in response to the activation of the anode by electronic action established by the operation of the cathode l3, said electronic action consisting of the impingement of electrons emitted by the cathode upon a target 4| forming a part of the anode l5. Electronic impingement on the target results in the generation of relatively large quantities of heat at the target, which is dissipated thence through the body of the anode l5. When in operation, the temperature of the X-ray generator, and particularly the anode, may be of the order of 500 centigrade and above. It should be understood, also, that X-ray generators are conditioned for operation by exhausting from the envelope substantially al-lgaseous and other impurities byevacuating the envelope, as by means of a molecular exhaust pump, and finally sealing the envelope in evacuated condition.

It is desirable that the target 4| be rotated at high speed in order to minimize the danger of over-heating the target itself at the point of electron impact. Considerable difiiculty is encountered in providing suitable support for the rotating element l5, since it is desirable to support the element in precise alignment for high speed rotation substantially without vibration throughout extended service periods. It is not feasible to utilize ordinary lubricants which evaporate, under the excessively high temperature and excessively low pressure conditions necessarily maintained within the envelope, and therefore will not remain in the bearings butwill dissipate throughout the envelope, thus not only robbing the bearings of lubrication, but also impairing Vacuum conditions in the tube and ren dering the same inoperative.

My present invention includes the provision of means for lubricating the bearings in a manner avoiding the aforesaid difiiculties, so that the device I5 may be supported for high speed, substantially frictionless rotation within the envelope.

Under ordinary circumstances, an X-ray generator remains in operation for but short intervals of time, of the order of a few seconds, sufficient to accomplish the making of X-ray photographs. During such operation, the anode I5 is first brought to operating speed, as by means of a suitable motor, at which time the tube energizing system connected with the anode and cathode is actuated for the production of X-rays through electronic impingement upon the target 4|, the X-ray exposure being made while the tube is in operation. Immediately upon the completion of the exposure, the tube energizing system is disabled and the anode driving means is de-energized. As a safety precaution, means is. ordinarily' provided for insuring that the anode isrotating at full operating speed throughout the period of the tube energizing system. The anode, being of appreciable mass and supported on substantially frictionless bearing means, will tend to continue to rotate for an appreciable interval, of the order of several minutes, even after the anode driving means has been de-energized, there being little, if any, braking effect due to windage in the evacuated envelope.

Naturally, the service life of an X-ray tube having a rotating anode, to some extent, depends upon wear in the anode bearings, which is relatively rapid in X-ray tubes in which the bearings are subjected to the excessive heat conditions developed as a result of the operation of the device. The service life of the bearings is further shortened due to the fact that lubrication, in the ordinary sense, cannot be provided where bearings are in operation under the substantial vacuum conditions prevailing in X-ray tubes. In order, therefore, to conserve the bearings and to lengthen the useful life of the X-ray tube, I provide not only for adequately lubricating the bearings, but also provide means in the anode structure itself for rapidly braking the anode to stand-still condition in order to reduce coasting time and resultant bearing wear after the termination of the period of useful rotation.

As shown in the drawing, the anode |5 comprises a cylindrical body 39 having an open end extending in the annular envelope space 25 in position to encircle the seal 34. The anode thus forms a shield for protecting the seal 34 from deterioration through impingement of stray electrons thereon. The opposite end of. the anode body is enclosed and afiords a mounting for the target 4!. In the illustrated embodiment, the target 4| comprises an annular ring of suitable target material, such as tungsten, which is embedded and secured in the preferably copper body of the anode IS. The anode body is formed with a groove 42 at the marginal edge of the end wall of the anode outwardly of the outer edge of the ring 4|, and a suitable strengthening rim 44 is preferably set into the groove 42. The ring 44 may comprise a tungsten copper composition and is joined to the outer edge of the target ring 4| and to the main copper body of the anode at the surfaces of the groove 42. The strengthening ring 44 preferably comprises a sponge-like mass of tungsten or other suitable material, such as tantalum or molybdenum, characterized by high melting temperature, with a preferably cuprous, tough, crack-resisting alloy filling the pores of said sponge-like mass. As a filler, I may use a predominantly copper alloy containing a heat hardening constituent, the alloy also permissively and preferably containing a deoxidating medium to promote wetting with tungsten. Any suitable hardening medium, such as chromium or cobalt, may be employed as the heat hardening constituent, and I may use beryllium, lithium, boron, calcium, or other suitable wetting agent. A satisfactory alloy formula is:

Per cent by weight Copper 98.5 Beryllium 1.0 Calcium 0.5

The ring 44 may be made by pressing a homogeneous mixture of tungsten and the copper alloy in powdered condition to form a pressed ring. This ring may then be sintered to form the finished ring of appropriate shape. The joining of the parts 39, 4| and 44 may be accomplished as a casting process by pre-forming the target ring 4| and then the reinforcing ring 44, then assembling the parts in a suitable mold and casting the copper body 39, which may comprise an alloy similar to that used as a. filler in the ring 44. The material of the ring thus has a coefficient of thermal expansion intermediate that of the target and body so that the tendency for cracking between the target and the body is greatly minimized.

The pedestal portion 29 extends within the cylindrical body of the anode and carries anode bearings comprising, in the illustrated embodiment, a pair of roller bearings 43 and 45 in spaced-apart position on the pedestal portion 29. Each bearing comprises an outer race secured preferably in the hollow pedestal, and an inner race secured on and thereby supporting a spindle 41, suitable roller members being conventionally retained between the inner and outer race portions of the bearings.

The spindle 41 may, of course, be secured in the bearings in any suitable or preferred fashion, although I have shown the same as being formed with threaded portions receiving clamping nuts for clampingly securing the inner bearing races in spaced relationship on the spindle 41, the outer races of the bearings 43 and 45 being secured. in the cavity 35, the outer race of the hearing 43 being secured in a seat 49 formed near the bottom of the cavity, said race being held in said seat by a spacing tube 5|, one end of which engages the outer race of the bearing 43 to hold it on the seat 49. The other end of the tube 5| forms a seat for receiving the outer race of the bearing 45, which is held in place by a clamping tube 53 having a flange portion 55 secured to the inner end of the pedestal portion 29 as by means of holding screws 51. The spindle 47 is thus journaled for rotation in the bearings 43 and 45 which are mounted on the pedestal portion 29. The stem 47 has an end formed with a flange 59 outwardly of the open end of the pedestal portion 29. The anode i is secured on said flange 59 by means of an annular mounting frame 6|, which is formed at one end for clamping on the flanged end of the stem 41. To this end, the frame El has an end wall 63 formed with an opening defined by a boss 65 for receiving the end of the stem 41 outwardly of the flange 59, the frame 6| being secured on the stem 41 by means of a bolt 61 threading into the stem 41 and having a head overlying the boss 65 to thereby clamp the wall 63 upon the flange 59. The frame 6| comprises cylindrical portions preferably formed integrally with the wall 63 and extending thence outwardly of and encircling the pedestal portion 29, said frame 6| having an enlarged annular portion 69 adapted snugly to extend within the cylindrical portion 39 of the anode l5, which is formed with a shoulder ll defining a seat for receiving the frame portion 69, the anode being anchored on the frame as by means of holding screws 12.

In order to lubricate the bearings, I provide for the application thereto of a lubricating medium which has a vapor pressure sufficiently low so that it will not evaporate from the bearing under the conditions of temperature and pressure prevailing within the envelope. To this end, I may utilize, as a lubricating medium, a material such as barium, caesium, strontium, cadmium, chromium, copper, silver, aluminum, iron or nickel, which have a vapor pressure of the order of l0 mm. of mercury at temperatures of the order of 200 Centigrade, whereby the lubricating medium may not migrate from a treated bearing operating under low pressure and high temperature conditions. In practicing this phase of my present invention, I provide for applying the selected lubricating medium in lm-like form upon the bearings after the same have been assembled in place and the envelope evacuated. The selected material or materials are applied upon the bearing surfaces by vaporizing the same and directing the vaporized material upon the bearing surfaces to be treated, whereby to condense the vapor as a thin film upon the Working surfaces of the bearings. The deposited material forms an alloy with the material of the bearings, which may be any suitable ferrous material, whereby is formed an alloy film having desired lubricating properties.

vaporization and delivery of the bearing material upon the surfaces to'be treated may be accomplished in any suitable or preferred manher. A supply of the material, for example, may be positioned in a capsule or container, having an opening facing the surfaces to be treated, and the material then heated in the capsule, as by the passage of an electric current, in order to vaporize the material within the capsule and blow the resulting vapor from the capsule and onto the surfaces to be processed. The bearing material may be formed as a filamentary wire in which the desired lubricating medium is incorporated and vaporized upon the bearing surfaces by passing an electric current through the wire. I prefer, however, in treating bearings for use in X-ray generators, to employ a hollow filamentary wire of iron or nickel containing,

within the hollow wire, a quantity of lubricating material such as barium, the hollow wire being weakened by reducing its wall thickness along a side of the wire facing the bearings to be treated. By passing an electrical current through the wire, the material therein may be vaporized and vapor products projected through the weakened wall section upon the bearing surfaces.

As shown in the drawing, the pedestal portion 29 and the spacing tube 5| are cut away to form openings 13 and 15, respectively, adjacent the bearings 43 and 45. In these openings are disposed loops 1! and 19 of hollow wire containing lubricating material, said loops T! and 19 being disposed with weakened wall portions facing the bearings 43 and 45. One end of each loop is electrically connected, as at 8| on the pedestal portion 29, the other end of each loop being electrically connected, as at 82, with conductors 83 which extend outwardly of the envelope through ducts formed in the plate 32, said conductors being hermetically sealed and electrically insulated in said ducts by glass-to-metal seals 85. By connecting a suitable source of electrical potential between the outwardly exposed end 21 of the pedestal and either or both of the conductors 83, an electrical heating current may be caused to flow through the wire in order to raise the temperature thereof to a point at which the lubricating material therein may be vaporized, and, as heretofore described, expelled through the weakened wall portion of the loops and onto the bearings. The bearings may thus be lubricated, and the quantity of lubricating material applied to each bearing may be regulated by controlling the activating current delivered through each loop. Each loop, furthermore, may be supplied with suflicient lubricating medium to enable re-lubrication of the bearings from time to time during the service life of the device.

In order to provide for making the anode to bring it rapidly to stand-still condition from operating speed, I provide magnetic means on the stationary and rotatable portions of the anode support adapted to function as a magnetic brake. The magnet may, of course, be applied on either one of the relatively rotatable members in position to magnetically influence the other, and, as shown in the drawing, the brake comprises a magnet 8"! fastened on the stationary pedestal in position to magnetically co-operate with a member of magnetic material on the anode, this co-operating member of magnetic material conveniently comprising the anode support frame 6!, which may be formed of steel or other suitable material adapted to form a magnetic circuit with the magnet 81.

As shown, the magnet 37 comprises a bar of permanently magnetized material characterized by the ability to retain magnetic properties at the operating temperature of the anode. Alnico is a suitable material for the purpose. The permanent magnet 81 is anchored in a slot 89 formed longitudinally in the external surfaces of the pedestal portion 29, suitable fastening straps 9| being employed to anchor the bar in the slot. The bar 81, at its opposite ends, is formed to receive the straps 9|, the medial portions of which are arranged to form magnet shoes 93 and 95, having surfaces snugly underlying the inner walls of the frame 6|, whereby a magnetic circuit, including the magnet 81, the shoes 93 and 95, and the portion of the frame 6| extending between the shoes, will be estab lished. This magnetic circuit will at all times tend to prevent relative angular movement between the pedestal on which the magnet 81 is clamped and the anode I5 which is secured to the frame 6i. This tendency to prevent relative rotation between the parts, oi course, is not sufficient to prevent rotation of the anode at operating speed when the anode driving motor is in operation. However, as soon as the anode driving motor is disabled, the magnetic brake, afiorded by the permanent magnet 8'! and the cooperating frame iii of magnetic material, will brake the anode to stand-still within a period of the order of a fraction of a minute.

The formation of the frame 6! of steel, in combination with the formation of the anode with a cylindrical skirt of cuprous material embracing the frame 6!, enables me to utilize the anode assembly as the rotor of an electric motor having stationary motor windings 99 arranged in annular form and disposed about the envelope extension 2! in which the anode structure is disposed. By energizing the windings from a suitable source of electrical power externally of the envelope, a rotating electromagnetic effect may be established within the envelope portion 2!, and the anode thus caused to rotate.

It is thought that the invention and its numerous attendant advantages will be fully understood from the foregoing description, and is obvious that numerous changes may be made in the form, construction and arrangement of the several parts without departing from the spirit or scope of the invention, or sacrificing any of its attendant advantages, the form herein disclosed being a preferred embodiment for the purpose of illustrating the invention.

The invention is hereby claimed as follows:

1. An X-ray tube having a sealed envelope, a rotary structure in said envelope comprising a support member, a rotary member on said support member, magnetic brake means comprising a permanent magnet on one of said members, and a co-operating element on the other member and forming, with said permanent magnet, a magnetic circuit whereby normally to resist relative angular movement between the support member and the rotary member.

2. An X-ray tube having a sealed envelope, a rotary structure in said envelope comprising a support member, a rotary member on said support member, a permanent magnet on said support member, means on said rotary member and forming a magnetic circuit with said magnet whereby normally to resist relative angular movement between the support member and the rotary member.

3. An X-ray tube having a sealed envelope, a rotary structure in said envelope comprising a support member, a rotary member on said support member, a permanent magnet anchored on one of said members, circuit-forming means anchored on the other member and forming a magnetic circuit with said permanent magnet, and magnet shoes on said permanent magnet and extending to form small gaps with said circuitforming means whereby to establish a magnetic circuit on the support member and on said rotary member tending normally to resist relative angular movement between the members.

4. An X-ray tube having a sealed envelope, a rotary structure in said envelope comprising a hollow support member formed with a cavity having an opening, a stem journaled in said cavity and having an end projecting at said opening, rotatable means secured on the projecting end of the stem and having portions, including portions of magnetic material, spaced outwardly of and encircling said support member, and a permanent magnet on said support member within said embracing portions of magnetic material.

5. An X-ray tube having a sealed envelope, a rotary structure in said envelope comprising a support member, means forming a rotary anode member supported on and having hollow portions embracing the support member, said hollow portions being spaced outwardly of the support member, and magnetic brake means comprising a permanent magnet on one of said members and a co-operating element on the other member and forming, with said permanent magnet, a magnetic circuit whereby normally to resist relative angular movement between the support member and the rotary anode member, said permanent magnet and said co-operating element being disposed within the space defined between the support member and the hollow portions of the anode member.

6. An X-ray tube having a sealed envelope, a rotary structure in said envelope comprising a hollow support member for-med with a cavity having an opening, a stem journaled in said cavity and having an end projecting at said opening, a rotatable support frame secured on the projecting end of the stem and having portions, including portions of magnetic material, spaced outwardly of and encircling said support member, a permanent magnet on said support member within said embracing portions of magnetic material, and means forming an anode secured on said rotatable support frame.

7. An X-ray tube having a sealed envelope, a rotary structure in said envelope comprising a support member, rotary means journaled on said support member and having portions, including portions of magnetic material, spaced outwardly of and encircling said support member, said support member being formed with a seat and a permanent magnet secured in said seat in position extending within said embracing portions of magnetic material.

ZED J. ATLEE. 

